Extracellular polysaccharides of endophytic fungus Alternaria tenuissima F1 from Angelica sinensis: Production conditions, purification, and antioxidant properties

Abstract

The yield, composition, structure and biofunction of microorganism exopolysaccharide (EPS) depended on their genetics and metabolic pathways. An EPS-producing endophytic fungus was isolated from Angelica sinensis planted in Dingxi, Gansu, China, and identified as Alternaria tenuissima F1. The production optimization, purification and characterization of the purified EPS from A. tenuissima F1 and the in-vitro antioxidant potentials was investigated. Results showed the optimal medium composition were 8% mannose, 2% yeast extract, 0.04% MgSO₄·7H₂O, 0.005% Vc, and the optimal cultivation conditions were set at initial pH 7.0, culture temperature 30 °C, inoculum size of 3%, 180 r/min for 5 d. The EPS purified by ion exchange column chromatography and gel chromatography was a non-reducing sugar and glycoprotein with pyranoid ring by Fourier transform infrared spectroscopy (FT-IR) analysis, displayed a porous network structure by scanning electron microscope (SEM) observation and exhibited a high thermal stability with the degradation temperature of 303.9 °C by thermogravimetric analysis (TG/DSC). Molecular weight of the purified EPS was 3.246 × 10⁴ g/mol, and EPS was composed of d-galacturonic acid, rhamnose, d-mannose, glucose, and d-galactose in ratio of 0.45:3.02:3.25:1.0:0.95. The EPS exhibited strong scavenging activity and may be a new source of natural antioxidant.

Keywords: Endophytic fungus exopolysaccharide; Production optimization and purification; Structure and bioactivities.